I doubt it's him having real troubles struggling with his sister and more that he doesn't have confidence while struggling with her. Either way, let's just enjoy the good ol' mindbreak.
"When you start a war about panties without even realise it"
@Plykiya I agree that good panties are softer but more expensive too. Some really good Boy underwears are almost like goods girl's boy shorts but cheaper. For the "lewder" part it's true but sometimes I'm not sure if men really care....